CEN method validation

Many experts in Europe have tested the methods of both standards with various pesticide-matrix combinations in their own laboratories. Consequently, the responsible working groups of CEN TC 275 concluded that these are the best methods available. Nevertheless, there is no complete validation of all possible pesticide-matrix combinations. However, for most multi-residue methods within the standards all those pesticides which had been successfully tested in method validation trials and/or proficiency tests are listed. Also, matrices which had been examined in ring tests are listed. 

Within CEN TC 275, a distinct protocol for the conduct of inter-laboratory method validation trials is not selected or required, but it is recommended to apply ISO 5725 or the ISO/International Union for Pure and Applied Chemistry (lUPAC) harmonized protocol. " In the past, results of several national and international interlaboratory trials had been accepted. Nevertheless, the following fundamental aspects of the harmonized protocol for the design of method-performance studies should be fulfilled ... 

The assessment of validation data of CEN methods does not differ significantly from other validation schemes. The most important quantitative performance characteristics are trueness and precision. Additionally, some information about sensitivity... 

The sensitivity achieved (LOD) is not normally presented. It is recognized that different laboratories determine dissimilar values for this parameter and even within a laboratory the repeatability of the LOD is low. Most often, the lowest validated concentration gives an impression about the lowest levels that can be analyzed generally with acceptable results. A measure of selectivity is the intensity of blank results. This intensity is discussed by the participants of inter-laboratory validation studies. However, results are not reported and limits are not defined by CEN TC 275. The results of method validations of the several multi-residue/multi-matrix methods are not reported in the same way, but newer methods with limited scope generate analogous tables with validation results (as an example, see Table 7). 

In Europe, very different concepts of method validation are in use. The extent of validation depends upon legal requirements (e.g., for enforcement methods provided by the applicant), upon the required level of acceptance (e.g., for CEN methods) and upon national resources. Undoubtedly, the best method validation is performed with the help of inter-laboratory studies of performance, but such studies can be uneconomic, too slow to reach completion or restricted in scope. 

The integration of analytical methods in European standards requires their acceptance by several national experts within special working groups and in a final weighted vote of National Standards Bodies. Therefore, there needs to be very high confidence in the performance of methods. Consequently, methods should be tested in inter-laboratory method validation studies, with the exception of those multiresidue methods which are widely used throughout Europe. In the case of CEN methods there is no doubt about residue definition but detailed requirements about the number of matrices and concentration levels in validation experiments do not exist. Eor this reason it may be that CEN methods are validated for important crops only. 

Significant progress has been made in the field of analytical detection of irradiated food to improve consumers confidence and to assist international trade of irradiated food [135,136]. Due to national and international programs and activities of the European Committee for Standardization (CEN), five validated and standardized detection methods are now available. The CEN is also considering the adoption of further five detection methods three will be screening methods (positive results from a screening method must be confirmed using a standardized method) [136]. 

Food methods validated by a collaborative trial study and those validated using the single-laboratory approach have been adopted as national and international standards by, e.g. CEN, International Organisation for Standardisation (ISO), AOAC International and by the Joint FAO/WHO Codex Alimentarius Food Standards Programme. A number of EN Standards developed by CEN relate to the organisation of controls. It is however important to keep in mind that, in addition to the method performance criteria, economical and prevention strategy... 

The other two CEN standards, for the determination of dithiocarbamate/thiuram disulfide residues and for the quantitation of bromide, are also separated into parts, but, in contrast to the multi-residue methods, complete methods are presented in each different part. Owing to this different approach and the reduced number of analytes, it was possible to validate these methods fully. 

For standardised instrumental analytical methods, i.e. biomarkers, biosensors and bioassays, there are well-established standard protocols on the national level, e.g. under Association Francaise de Normalisation (AFNOR), British Standard Institute (BSI), DIN (German Organisation for Standardisation), etc., and all those standards are formed by ISO-Working Groups and by validation studies into ISO - and CEN - Standards. Normal accredited and well-qualified laboratories should be able to perform the monitoring. 

Recognised test methods include methods developed by internationally recognised agencies such as DIN, ISO, CEN or OECD. As a general principle, the lowest test result for the most sensitive species has to be used as the starting point for the risk assessment and for the derivation of the water and biota quality norms. The toxicity data used for the risk assessment have to be examined critically with respect to validity and relevance. 

Many of the more established techniques have been validated through collaborative studies which becomes of greater importance as laboratories seek to become accredited via ISO, EN or related systems where the use of official or well validated methods is mandatory. New instrumental techniques are constantly being reported in the literature but it often requires many years before procedures are introduced, validated and then applied within the food industry. Recent techniques that can be included in this category are capillary electrophoresis and liquid chromatography-mass spectrometry (LC-MS). In time procedures based on these techniques will also become accepted as routine methods and are likely to be adopted by some of the official international bodies like the AOAC International, CEN, ISO, etc. 

Standard methods of analysis published by bodies such as the American Society for Testing and Materials (ASTM), de Normalisation (CEN), or ISO are rigorously tested and validated in method performance, or validation, studies. These interlaboratory trials can establish reproducibility and method bias and also give some confidence that the method can be used in different environments. Laboratories are chosen with an expectation that they can competently follow the proposed method, which will have already been extensively validated before an interlaboratory trial is contemplated. To this end, a pilot trial is sometimes undertaken to ensure the method description can be followed and to give an initial estimate of the precision of the method. 

Continuing with the above example of ER3 of the European Construction Products Directive horizontal emissions test methods (i.e., applicable to multiple product types) have been developed by CEN and ISO for compliance with the CPD and are now available as parts 6, 9,10 and 11 of EN/ISO standard 16000 (see Table 6.1). Furthermore, a program of work led by CEN TC351 has now been instigated under European Council Mandate M/366 to amalgamate and validate these standards. Once this work is completed (estimated 2010) it is understood that chemical emissions testing will become a mandatory part of CE marking for construction products. 

Once the method has been established and validated, it should be described in full detail such that it can be carried out by any other analyst. Besides the numerous experimental details relating to the chemicals, solvents and solutions used and the chromatographic parameters, important observations such as for instance the findings about the stability of standard solutions should be laid down appropriately in the method description as notes or remarks. But potential health risks to the analytical operator should also be addressed, for instance in a warning note at the beginning of the method description. The following structure of a method description, which was agreed upon as a CEN standard format, is a recommended example. 

To support the analyst in applying such controls, CEN (the European Standardisation Commission) has in TC 194 adopted and validated analytical methods for the determination of the overall migration and the migration of some specific substances. These methods are intended to be applied for testing plashc materials and articles. At national level, e.g., in The Netherlands, the methods and simulants may also be used to demonstrate compliance with national regulation of non-plastic or multilayer materials composed of plastics and non-plastics (e.g. plastic on paper, coating on metal). 

Due to the demand for reliable and comparable methods, performance requirements have been established at a national and international level for implementation of official methods, e.g. by European legislation, by the CEN or the Association of the Analytical Communities (AOAC) International, and worldwide by Codex Alimen-tarius (CAC). Thus any method proposed to be used for official purposes must be validated in a collaborative trial study, resulting in defined method performance characteristics [4], The framework for the design and conduct of such collaborative trial studies, as well as the statistical evaluation, are also defined in appropriate protocols [5]. Any method that has been successfully validated according to these protocols can be recognised as an official method for use in legal cases or for international trade control purposes. 

Reference or standard consensus methods methods developed by organisations that use interlaboratory studies to validate them (ISO, CEN, AOAC, DIN, BSI, AFNOR etc.). Their development leads to a known and stated precision or accuracy. 

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